To Reply any Incoming Message in your Google Talk Messenger Service, you may need to install and use GTalk Auto Reply. This GTalk Application would help you to answer or response any incoming message automatically with the text message that you have to add before.
Download Google Talk Auto Reply Software | Source Code
License: Open Source / Free
Website: gtalkautoreply.codeplex.com
Installation

Download the gtalk auto response software and run setup.exe
Use your gtalk account with its password to login and set the auto reply message that you want.
Done

If you looking for an alternative IM client for Windows Live Messenger or Chat Client for MSN Messenger in the ways you wanna chat with your friends through WLM, you can try the third party chat client called as emesene
Features of emesene
Emesene compatible with Windows Live Messenger 9 or 16. You can also use webcam, use proxy, tabbed chat, offline messaging, nudges, file transfer, avatar, emoticons (customizable) and many more. Changing theme, smiley, sound, GUI are the features that you can do with emesene.
Version History emesene
The latest version of emesene …

Microsoft has decided to retired MSN / WLM Web Messenger on June 30th 2009. Therefore if you visit to webmessenger.msn.com you’ll only see a notification that Windows Live Messenger / MSN Web Messenger on the web has moved.
Windows Live Messenger on the web has moved!
Messenger is really about people – so the web version is now built into Hotmail and the rest of Windows Live. Go to http://people.live.com to see who’s online.
You can also see if your friends are online just by glancing at your inbox. You can turn e-mails …